I have another, mor serious problem.
In my configurartion I used to have the Box folder (c:\users\{username}\Box) as an item and all worked fine.
Noted days ago that items on the Box tree did not show up on searches.
Imagined the problem could be related to the one above and applied a simple fix that worked for some: uninstall Box, then Everything and reinstall both.
Now I can't even add Box to Folders list:

If I click Continue things get worse:

It seems that file structure is OK - chkdsk /f c: has been used.
No known corruptions (sfc /scannow results OK).
Any clue?